Automatic Position Reporting System for HF
APRS Network
The Automatic Position Reporting System (APRS) network comprises:
- RF User - Equipped with a base station transceiver and APRS Terminal Node Controller (TNC)
- Portable User - Equipped with an APRS-compatible Hand-Held radio
- Mobile User - Equipped with a mobile transceiver and APRS TNC
- Weather Station - Conneted via the Ineternet
- Fill-In Digipeater - Provides extra coverage for a Wide Repeater
- Wide Digipeater - Wide area node
- IGate - Equipped with a base station transceiver, APRS TNC and Internet connection
- APRS Database and Web Server - APRS Internet Service (APRS-IS)
- Internet User - Mobile Device with APRS app connected to the Internet
![](images/network.jpg)
The APRS Network
APRS Description
The APRS defines:
- Stations, for broadcasting location, telemetry data, text over both RF and Internet networks
- Nodes, which are identified by Callsign-SSID format
- Each node can store and forward messages
- Messages, which are unnumbered AX.25 datagrams
- The message “Path” contains a routing list
- Digipeaters modify the Path to avert the “ping-pong” effect
APRS Secondary Station ID (SSID)
Each APRS node uses a callsign with a SSID suffix, identifying its purpose:
-0 (No SSID) Home Station-1 Digipeater, or Home Station running a Fill-In Digi,-2 Digipeater [#2] on 70CM-3 Digipeater [#3]-4 HF to VHF Gateway-5 IGate (Dedicated system, not home station)-6 Operation via Satellite-7 Kenwood D7 Handheld-8 Secondary Mobile usage (also Maritime vessels) (VHF / UHF)-9 Mobiles (VHF / UHF)-10 Operation via Internet Only (No RF capability)-11 is for APRStouch-tone users (also high altitude balloons)-12 Portable Units such as Laptops, Camp Sites etc-13-14 Interstate Truckers-15 Operation via HF
APRS Paths
The APRS path is a routing list for the message: VK3ABC-1, VK3XYZ-1, etc
- Can use callsign aliases for special nodes: WIDE1-1, WIDE2-1
- The SSID of aliases sets the number of hops allowed
- The path is modified by each digipeater
- The SSID is decremented in each hop, but -0 is omitted.
- An asterisk (*) signifies when a callsign or alias was used
- Example:
- WIDE1-1, WIDE2-2 (Original path)
- <callsign1>*, WIDE2-2 (First hop)
- <callsign1>, <callsign2>, WIDE2-1* (Second hop)
- <callsign1>, <callsign2>, <callsign3>* (Third hop)
APRS Rules for HF
There are special rules for APRS used on HF, primarily because HF, unlike VHF/UHF, presents a very wide area network.
- No Digipeating on HF!
- Most receiving Gateways will route to APRS-IS
- So, Path = WIDE1-1 is sufficient
- Use 300 Baud, 200Hz FSK, 1600Hz/1800Hz
- For SSB must be spot on frequency
- LSB & USB both work because AX.25 is NRZI
- Avoid any ALC action on TX to limit distortion
- Beacon time ≥ 10 minutes: Permits up to 70 users
- Good luck – Because APRS has no ACK or FEC
APRS Frequencies and Gateways
There are defined frequencies used for APRS. However the APRS stations may change over time.
40m 7048.600kHz LSB
VK2IO-4 Sydney Primary Net Station (also 7.047.17 LSB)VK7HSE-4 Kingston Secondary Net Station
30m 10147.600kHz USB
VK1IAN-1 Canberra RX OnlyVK2ACW-1 OrangeVK2HL-1 Sydney Part Time RX OnlyVK2IO-4 Sydney OfflineVK2OL-5 Sydney Full Time RX OnlyVK2ZSZ-4 Queanbeyan Full Time RX OnlyVK2ZZM-5 Sydney Full Time RX OnlyVK3MY-4 Melbourne Primary Net stationVK4AB-4 Ipswich Full TimeVK4DMI-4 Pine Rivers Secondary Net stationVK4MQ-5 Toowoomba Full Time RX OnlyVK4RM-4 Mackay Full TimeVK4UN-4 Tewantin Full TimeVK5RR-4 WaikerieVK6LD-4 Perth Full TimeVK7ZRO-4 Bothwell Full TimeVK8KMD-10 Alice SpringsZL3GR-4 Tauranga RX Only
20m 14103.00kHz LSB
VK2IO-4 Sydney Offline
APRS TNC Pin Assignments
We use an Argent Data Systems T3 Mini TNC board. This is an excellent device with a good configuration tool. It has a wide variety of input/ouput pins, suitable for communications, control and telemetry.
![](images/t3Mini.jpg)
Argent Data Systems T3 Mini TNC
Pin Assignments:
- A1-A4 Analog inputs 1-4 (max voltage 4xVdd)
- 1W Dallas 1-Wire data bus
- SQL Squelch input
- AUX Auxiliary I/O pin
- GND Ground
- RST Reset (active low)
- B-RX Serial port B input
- B-TX Serial port B output
- A-RX Serial port A input
- A-TX Serial port A output
- CFG Configuration select
- AOUT Audio output (to radio)
- AIN Audio input (from radio)
- GRN Green LED output for external LED
- RED Red LED output for external LED
- PTT Push-to-talk (open collector)
- 5V Regulator output or Vdd input, 5v max, 2.8v min
- VIN Unregulated supply voltage, 6v to 28v
- GP1-GP12 General purpose digital input/output pins
TNC Configuration Tool
Argent Data Systems T3 Mini TNC board comes with OpenTracker - a versatile configuration tool.
![](images/config.jpg)
OpenTracker TNC Configuration Tool
APRS TNC Wiring
The Argent Data Systems T3 Mini TNC board connects directly to a Serial TTL GPS Receiver. We use solderable enamelled copper wire to interconnect such devices.
![](images/wiring.jpg)
Argent Data Systems T3 Mini TNC - Ublox NEO-6M GPS Receiver - GPS Patch Antenna
A 5V regulator and two audio line transformers complete the design for connecting the TNC to a radio transceiver.
![](images/schematic_ono5w6uj.jpg)
Pictorial Schematic Diagram
APRS TNC Assembly
The components are assembled into a Hammond H9004 ABS Enclosure. The transformers and regulator are glued to the base. A sleeved grommet is used for the CAT-5 cable.![](images/assembly1_a7g6ff8z.jpg)
![](images/assembly1_a7g6ff8z.jpg)
APRS TNC Assembly 1
The completed APRS TNC dongle needs to have a clear view of the sky. It will starts transmitting when a 3D GPS fix is valid.
![](images/assembly2_krdwyeil.jpg)
APRS TNC Assembly 2
APRS Display
The resulting APRS data, relayed to the Internet by an IGate, is easily displayed on the aprs.fi website.
![](images/map.jpg)
APRS Station Info
By querying the aprs.fi website additional station information can be displayed.
![](images/info.jpg)
References
- APRS GippsTech 2017 Presentation
- http://www.aprs.org
- http://www.aprs.net.au
- https://info.aprs.net
- https://aprs.fi
- https://www.argentdata.com